Supercritical drying method for semiconductor substrate

ABSTRACT

In one embodiment, after rinsing a semiconductor substrate having a fine pattern formed thereon with pure water, the pure water staying on the semiconductor substrate is substituted with a water soluble organic solvent, and then, the semiconductor substrate is introduced into a chamber in a state wet with the water soluble organic solvent. Then, the water soluble organic solvent is turned into a supercritical state by increasing a temperature inside of the chamber. Thereafter, the inside of the chamber is reduced in pressure while keeping the inside of the chamber at a temperature enough not to liquefy the pure water (i.e., rinsing pure water mixed into the water soluble organic solvent), and further, the water soluble organic solvent in the supercritical state is changed into a gaseous state, to be discharged from the chamber, so that the semiconductor substrate is dried.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2010-254922, filed on Nov. 15,2010, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to a supercritical dryingmethod for semiconductor substrate.

BACKGROUND

Processes for fabricating a semiconductor device variously include alithography process, an etching process, an ion implantation process,and the like. After completion of one process and before transfer to thefollowing process, cleaning and drying processes for removing impuritiesor residues remaining on a wafer and cleaning the surface of the waferare carried out.

In, for example, a wafer cleaning process after an etching process, achemical solution for cleaning is supplied to the surface of the wafer,and thereafter, pure water is supplied, followed by a rinsing process.After the rinsing process, the pure water remaining on the wafer isremoved, followed by a drying process for drying the wafer.

As a method for the drying process has been known, for example, a methodfor drying a wafer by substituting the pure water remaining on the waferwith isopropyl alcohol (IPA). However, there has arisen an issue of acollapse of a pattern formed on the wafer due to surface tension of aliquid during the drying process.

In order to solve the above-described issue, supercritical drying undersurface tension of zero has been proposed. For example, a wafer whosesurface is wet with IPA is immersed in carbon dioxide (a supercriticalCO₂ fluid) in a supercritical state inside of a chamber, so that IPA onthe wafer is dissolved in the supercritical CO₂ fluid. Then, thesupercritical CO₂ fluid having IPA dissolved therein is graduallydischarged from the chamber. Thereafter, the inside of the chamber isreduced in pressure and temperature, and then, the supercritical CO₂fluid is changed to a gaseous phase, to be discharged outside of thechamber. Consequently, the wafer is dried.

However, there has arisen an issue that when carbon dioxide is changedfrom the supercritical phase to the gaseous phase by reducing thepressure inside of the chamber, IPA remaining inside of the chamber inthe state dissolved in the supercritical CO₂ fluid is coagulated andadsorbed again on the wafer, thereby producing particles (dryingstains). Moreover, in order to satisfactorily discharge IPA dissolved inthe supercritical CO₂ fluid from the inside of the chamber, thesupercritical CO₂ fluid is necessarily continued to be supplied to thechamber, and further, the supercritical CO₂ fluid having IPA dissolvedtherein is necessarily continued to be gradually discharged in a smallquantity, thereby raising an issue that a time required for the dryingprocess becomes longer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating the interrelationship among a pressure, atemperature, and the phase of substance;

FIG. 2 is a diagram schematically illustrating a supercritical dryingdevice in a first embodiment according to the present invention;

FIG. 3 is a flowchart illustrating a supercritical drying method in thefirst embodiment according to the present invention;

FIG. 4 is a graph illustrating a steam pressure curve in therelationship between a water soluble organic solvent and pure water;

FIG. 5 is a flowchart illustrating a supercritical drying method in asecond embodiment according to the present invention; and

FIG. 6 is a graph illustrating a steam pressure curve in therelationship between a water soluble organic solvent and a waterinsoluble organic solvent.

DETAILED DESCRIPTION

In one embodiment, after rinsing a semiconductor substrate having a finepattern formed thereon with pure water, the pure water staying on thesemiconductor substrate is substituted with a water soluble organicsolvent, and then, the semiconductor substrate is introduced into achamber in a state wet with the water soluble organic solvent. Then, thewater soluble organic solvent is turned into a supercritical state byincreasing a temperature inside of the chamber. Thereafter, the insideof the chamber is reduced in pressure while keeping the inside of thechamber at a temperature enough not to liquefy the pure water (i.e.,rinsing pure water mixed into the water soluble organic solvent), andfurther, the water soluble organic solvent in the supercritical state ischanged into a gaseous state, to be discharged from the chamber, so thatthe semiconductor substrate is dried.

Embodiments will be described below with reference to the attacheddrawings.

First Embodiment

First, a description will be given on supercritical drying. FIG. 1 is agraph illustrating the interrelationship among a pressure, atemperature, and the phase of substance. The functional substance of asupercritical fluid for use in the supercritical drying is present inthree phases: a gaseous phase (gas); a liquid phase (a liquid); and asolid phase (a solid).

As illustrated in FIG. 1, the above-described three phases arepartitioned by a steam pressure curve (i.e., a gaseous phase equilibriumline) indicating the boundary between the gaseous phase and the liquidphase, a sublimation curve indicating the boundary between the gaseousphase and the solid phase, and a dissolution curve indicating theboundary between the solid phase and the liquid phase. A triple point isreferred to as a point at which the three phases overlap. When the steampressure curve extends toward a high temperature side from the triplepoint, the curve reaches a critical point indicating a limit at whichthe gaseous phase and the liquid phase coexist. The gaseous phase andthe liquid phase are equal in density at this critical point, andtherefore, an interface on which gas and liquid coexist is dissipated.

At temperatures and pressures higher than those at the critical point,the gaseous phase and the liquid phase are not distinguished from eachother, so that substance is turned into a supercritical fluid. Thesupercritical fluid is a fluid compressed densely at a temperaturehigher than a critical temperature. The supercritical fluid is similarto gas from the viewpoint in which the diffusion force of solventmolecules is dominant. At the same time, the supercritical fluid issimilar to a liquid from the viewpoint in which an influence bycoagulation force of the molecules should be considered, and therefore,the supercritical fluid has a property capable of dissolving variouskinds of substances.

In addition, the supercritical fluid has a much higher infiltrationproperty than that of a liquid, and has the characteristics capable ofreadily penetrating even a fine structure.

Furthermore, the supercritical fluid can be dried in such a manner as tobe transited from the supercritical state directly to the gaseous phaseto prevent any presence of the interface between the gas and the liquid,that is, to prevent capillary force (surface tension) from acting. Thus,drying without breaking a fine structure can be achieved. Supercriticaldrying is to dry a substrate by utilizing the supercritical state of thesupercritical fluid.

Next, referring to FIG. 2, a description will be given of asupercritical drying device for supercritically drying a semiconductorsubstrate. As illustrated in FIG. 2, a supercritical drying device 10 isprovided with a chamber 11 incorporating a heater 12 therein. Thechamber 11 is a high pressure vessel made of SUS or the like. The heater12 can adjust the temperature inside of the chamber 11. FIG. 2illustrates the configuration in which the heater 12 is incorporatedinside of the chamber 11, and the heater 12 may be disposed at the outerperipheral portion of the chamber 11.

Inside of the chamber 11 is housed a stage 13 formed of a ring-like flatplate for holding therein a semiconductor substrate W which is to besubjected to a supercritical drying process.

To the chamber 11 is connected a pipeline 15, through which gas or asupercritical fluid staying inside of the chamber 11 can be dischargedto the outside. On the pipeline 15 is disposed a control valve 16 foradjusting the valve opening degree while monitoring and controlling apressure inside of the chamber 11. The closure of the control valve 16leads to a closely sealed state inside of the chamber 11.

Next, referring to a flowchart of FIG. 3, a description will be given ofmethods for cleaning and drying the semiconductor substrate in thepresent embodiment.

(Step S101) A semiconductor substrate to be processed is delivered to acleaning chamber, not illustrated. Then, a chemical solution is suppliedonto the semiconductor substrate, followed by cleaning. As the chemicalsolution may include a sulfuric acid, a fluoric acid, a hydrochloricacid, hydrogen peroxide, and the like.

Here, the cleaning process includes peeling a resist from thesemiconductor substrate, removing particles or metallic impurities,etching and removing a film formed on the substrate, and the like. Afine pattern is formed on the semiconductor substrate. The fine patternmay be formed before the cleaning process or may be formed during thecleaning process.

(Step S102) After the cleaning process in step S101, rinsing with purewater is carried out such that the pure water is supplied onto thesemiconductor substrate, and then, the chemical solution remaining onthe semiconductor substrate is rinsed with the pure water.

(Step S103) After the rinsing process with the pure water in step S102,liquid replacing is carried out such that the semiconductor substratewet thereon with the pure water is immersed in a water soluble organicsolvent, and thus, the pure water on the semiconductor substrate isreplaced with the water soluble organic solvent.

The water soluble organic solvent used herein may be, for example,alcohol such as isopropyl alcohol (IPA) or ketone which is higher insteam pressure than the pure water (i.e., lower in boiling point).Hereinafter, a description will be given of the case where IPA is usedas the water soluble organic solvent.

Incidentally, it is construed that in the liquid replacing process, thesemiconductor substrate is wet thereon with IPA, which includes the purewater (although in a small quantity) in mixture.

(Step S104) After the liquid replacing process in step S103, thesemiconductor substrate is delivered out of the cleaning chamber in thestate in which it is kept wet thereon with IPA but is not naturallydried. Thereafter, the semiconductor substrate is introduced to thechamber 11 illustrated in FIG. 2, and then, is fixed onto the stage 13.After that, the control valve 16 is closed, and thus, the inside of thechamber 11 is tightly closed.

(Step S105) IPA covering the surface of the semiconductor substrate isheated inside of the chamber 11 tightly closed by using the heater 12.An increase in IPA vaporized with the heat increases pressure inside ofthe chamber 11, which has a predetermined volume owing to the tightclosure, in accordance with a steam pressure curve of IPA indicated by abroken line in FIG. 4.

Here, the actual pressure inside of the chamber 11 is equal to the sumof partial pressures of all of gaseous molecules present inside of thechamber 11. However, in the present embodiment, the partial pressure ofgaseous IPA is regarded as the pressure inside of the chamber 11.

As illustrated in FIG. 4, when IPA is heated above a criticaltemperature Tc in the state in which the pressure inside of the chamber11 reaches a critical pressure Pc of IPA, IPA (gaseous IPA and liquidIPA) inside of the chamber 11 is turned to a supercritical state. Inthis manner, the chamber 11 is filled with supercritical IPA IPA in asupercritical state), and thus, the semiconductor substrate is coveredwith the supercritical IPA.

Incidentally, until IPA is turned into the supercritical state, thegaseous IPA and the liquid IPA are made coexist inside of the chamber 11such that all of the liquid IPA covering the surface of thesemiconductor substrate is not vaporized, that is, the semiconductorsubstrate is wet with the liquid IPA.

A temperature Tc, a pressure Pc, and the volume of the chamber 11 aresubstituted into a gas state equation (PV=nRT, wherein P designates apressure; V, a volume; n, the number of moles; R, a gas constant; and T,the temperature), so that the amount nc (mol) of IPA present in thegaseous state inside of the chamber 11 can be obtained when IPA isturned into the supercritical state.

Consequently, the liquid IPA need be present in nc (mol) or more insideof the chamber 11 before the heating is started in step S105. In thecase where the amount of IPA on the semiconductor substrate to beintroduced into the chamber 11 is less than nc (mol), the liquid IPA issupplied into the chamber 11 from a chemical solution supplying unit,not illustrated, so that the liquid IPA can be present in nc (mol) ormore inside of the chamber 11.

As the heating proceeds in step S105, the pure water staying on thesemiconductor substrate in mixture with the liquid IPA is beingvaporized, and therefore, the partial pressure of the pure water isincreased in accordance with the steam pressure curve of the pure waterindicated by a solid line in FIG. 4. The pure water is present in thegaseous state (i.e., the steam) in the amount based on the temperatureinside of the chamber 11, the steam pressure of the pure water at thattime, and the volume of the chamber 11, and further, in the liquid statein the residual amount. Since the pure water mixed into the liquid IPAis small in quantity, all or most of the pure water is construed to beturned into the steam.

(Step S106) After IPA is turned into the supercritical state in stepS105, the inside of the chamber 11 is further heated by using the heater12, and thus, it is increased up to a predetermined temperature Tw orhigher (see an arrow A1 in FIG. 4). The temperature Tw is thetemperature of the pure water (i.e., a boiling point) when a saturatedsteam pressure becomes the critical pressure Pc of IPA. The criticalpressure Pc of IPA is about 5.4 MPa, and therefore, the temperature Twbecomes about 270° C. At this time, all of the pure water staying insideof the chamber 11 is present as the steam.

(Step S107) After heating in step S106, the supercritical IPA stayinginside of the chamber 11 is discharged by opening the control valve 16,and thus, the inside of the chamber 11 is reduced in pressure (see anarrow A2 in FIG. 4). At this time, the temperature inside of the chamber11 is kept at the predetermined temperature Tw or higher.

When the pressure inside of the chamber 11 becomes the critical pressurePc or lower of IPA, the phase of IPA is changed from the supercriticalfluid to gas. Since the temperature inside of the chamber 11 is set atTw or higher, the pure water is kept gaseous even after the phase of IPAis changed, thereby preventing reliquefaction.

(Step S108) After the pressure inside of the chamber 11 is decreaseddown to the atmospheric pressure, the chamber 11 is cooled, and then,the semiconductor substrate is delivered out of the chamber 11.

Alternatively, after the pressure inside of the chamber 11 is decreaseddown to the atmospheric pressure, the semiconductor substrate at a hightemperature may be transported to a cooling chamber, not illustrated, asit is, followed by cooling. In this case, the chamber 11 can be kept ata certain high temperature all the time, thereby shortening the timerequired for drying the semiconductor substrate.

As described above, in the present embodiment, IPA covering the surfaceof the semiconductor substrate is changed from the liquid IPA to thesupercritical IPA, and thereafter, the supercritical IPA inside of thechamber 11 is dried in such a manner as to be directly changed in phaseto the gaseous IPA. Consequently, no capillary (i.e., the surfacetension) acts on the fine pattern formed on the semiconductor substrate,and therefore, the semiconductor substrate can be dried without breakingthe fine pattern.

Moreover, when the pressure inside of the chamber 11 is decreased sothat the supercritical IPA is changed in phase to the gaseous IPA, thetemperature inside of the chamber 11 is set to a value at which thesteam pressure of the pure water becomes higher than the criticalpressure of IPA, and thus, the pure water staying inside of the chamber11 is kept gaseous (i.e., the steam), to be prevented from being turnedinto a liquid state. In this manner, the steam inside of the chamber 11is liquefied to be adsorbed onto the semiconductor substrate, thuspreventing particles (i.e., drying stains) from being produced.

In the present embodiment, IPA staying inside of the chamber 11 isheated to be turned into the supercritical state, and further, thepressure inside of the chamber 11 is decreased while keeping thetemperature inside of the chamber 11 to Tw or higher, thereby drying thesemiconductor substrate. In contrast, in the conventional supercriticaldrying method, the supercritical CO₂ fluid is continuously supplied tothe chamber for a long period of time, and then, IPA on thesemiconductor substrate and inside of the chamber is sufficientlydissolved, to be discharged little by little. IPA is sufficientlydischarged from the chamber, and then, the pressure and temperature aredecreased inside of the chamber. In the present embodiment, it isunnecessary to perform the process requiring a long period of time, inwhich the supercritical CO₂ fluid having IPA dissolved therein isdischarged from the chamber little by little, unlike the conventionalsupercritical drying method, thus shortening the time required for thedrying process.

In this manner, with the supercritical drying method for thesemiconductor substrate in the present embodiment, it is possible toreduce the particles produced on the semiconductor substrate, andfurther, to shorten the time required for the drying process.

Although the description has been given of the example in which IPA isused as the water soluble organic solvent in the above-described firstembodiment, the same process may be performed even in the case of use ofa water soluble organic solvent other than IPA.

Additionally, although the temperature is increased up to Tw or higherinside of the chamber 11 in step S106, before the pressure inside of thechamber 11 is decreased in step S107 in the above-described firstembodiment, the decrease in pressure and the increase in temperatureinside of the chamber 11 may be achieved at the same time as long as thetemperature inside of the chamber 11 may become Tw or higher when IPA ischanged from the supercritical phase to the gaseous phase.

Second Embodiment

In the above-described first embodiment, after the semiconductorsubstrate is rinsed with the pure water (step S102), the pure waterstaying on the semiconductor substrate is replaced with the watersoluble organic solvent (step S103), and then, the semiconductorsubstrate wet thereon with the water soluble organic solvent isintroduced into the chamber 11 (step S104). In contrast, in the presentembodiment, after the pure water staying on the semiconductor substrateis replaced with the water soluble organic solvent, the water solubleorganic solvent staying on the semiconductor substrate is replaced witha water insoluble organic solvent before the semiconductor substrate isintroduced into the chamber 11. It is possible to reduce the cost of thechamber 11 by using an uninflammable water insoluble organic solvent incomparison with the first embodiment in which the flammable watersoluble organic solvent is used.

Referring to a flowchart of FIG. 5, a description will be given ofmethods for cleaning and drying a semiconductor substrate in the presentembodiment. Here, steps S201, S202, and S203 in FIG. 5 are similar tosteps S101, S102, and S103, respectively, and therefore, theirdescriptions will not be repeated below.

(Step S204) After the liquid replacing process in step S203, a liquidreplacing process is performed in which the semiconductor substrate wetthereon with a water soluble organic solvent (i.e., IPA) is immersed ina water insoluble organic solvent so that IPA staying on thesemiconductor substrate is replaced with the water insoluble organicsolvent.

The water insoluble organic solvent has a higher steam pressure (i.e., alower boiling point) than that of the water soluble organic solvent, andis exemplified by, for example, alcohol fluoride, hydrofluoroether (HFEsuch as AE-3000 (CF₃CH₂OCF₂CHF₂)), chlorofluorocarbon (CFC),hydrofluorocarbon (HFC), and perfluorocarbon (PFC). Hereinafter, adescription will be given on the case where HFE is used as the waterinsoluble organic solvent.

The semiconductor substrate is wet thereon with HFE in the liquidreplacing process. Here, HFE contains IPA in mixture, though in a smallquantity.

(Step S205) After the liquid replacing process in step S204, thesemiconductor substrate is delivered out of the cleaning chamber in thestate in which it is kept wet thereon with HFE but is not naturallydried. Thereafter, the semiconductor substrate is introduced to thechamber 11 illustrated in FIG. 2, and then, is fixed onto the stage 13.After that, the control valve 16 is closed, and thus, the inside of thechamber 11 is tightly closed.

(Step S206) HFE covering the surface of the semiconductor substrate isheated by using the heater 12 inside of the chamber 11 tightly closed.An increase in HFE vaporized with the heat increases a pressure insideof the chamber 11, which has a predetermined volume owing to the tightclosure, in accordance with a steam pressure curve of HFE indicated by abroken line in FIG. 6.

Here, the actual pressure inside of the chamber 11 is equal to the sumof partial pressures of all of gaseous molecules present inside of thechamber 11. However, in the present embodiment, the partial pressure ofgaseous HFE is regarded as the pressure inside of the chamber 11.

As illustrated in FIG. 6, when HFE is heated above a criticaltemperature Tc′ in the state in which the pressure inside of the chamber11 reaches a critical pressure Pc′ of HFE, HFE (gaseous HFE and liquidHFE) inside of the chamber 11 is turned to a supercritical state. Inthis manner, the chamber 11 is filled with supercritical HFE (i.e., HFEin a supercritical state), and thus, the semiconductor substrate iscovered with the supercritical HFE.

Incidentally, until HFE is turned into the supercritical state, thegaseous HFE and the liquid HFE are made coexist inside of the chamber 11such that all of the liquid HFE covering the surface of thesemiconductor substrate is not vaporized, that is, the semiconductorsubstrate is wet with the liquid HFE.

A temperature Tc′, a pressure Pc′, and the volume of the chamber 11 aresubstituted into a gas state equation (PV=nRT, wherein P designates apressure; V, a volume; n, the number of moles; R, a gas constant; and T,the temperature), so that the amount nc′ (mol) of HFE present in thegaseous state inside of the chamber 11 can be obtained when HFE isturned into the supercritical state.

Consequently, the liquid HFE need be present in nc′ (mol) or more insideof the chamber 11 before the heating is started in step S206. In thecase where the amount of HFE on the semiconductor substrate to beintroduced into the chamber 11 is less than nc′ (mol), the liquid HFE issupplied into the chamber 11 from a chemical solution supplying unit,not illustrated, so that the liquid HFE can be present in nc′ (mol) ormore inside of the chamber 11.

As the heating proceeds in step S206, IPA staying on the semiconductorsubstrate in mixture with the liquid HFE also is being vaporized, andtherefore, the partial pressure of IPA is increased in accordance withthe steam pressure curve of IPA indicated by a solid line in FIG. 6. IPAis present in the gaseous state in the amount based on the temperatureinside of the chamber 11, the steam pressure of IPA at that time, andthe volume of the chamber 11, and further, in the liquid state in theresidual amount. Since IPA mixed into the liquid HFE is small inquantity, all or most of IPA is construed to be turned into the gas.

(Step S207) After HFE is turned into the supercritical state in stepS206, the inside of the chamber 11 is further heated by using the heater12, and thus, it is increased up to a predetermined temperature Ts orhigher (see an arrow A3 in FIG. 6). The temperature Ts is thetemperature of IPA (i.e., a boiling point) when a steam pressure of IPAbecomes the critical pressure Pc′ of HFE. The critical pressure Pc′ ofHFE is about 2.4 MPa, and therefore, the temperature Ts becomes about200° C. At this time, all of IPA staying inside of the chamber 11 ispresent as the gas.

(Step S208) After heating in step S207, the supercritical HFE stayinginside of the chamber 11 is discharged by opening the control valve 16,and thus, the inside of the chamber 11 is reduced in pressure (see anarrow A4 in FIG. 6). At this time, the temperature inside of the chamber11 is kept at the predetermined temperature Ts or higher.

When the pressure inside of the chamber 11 becomes the critical pressurePc′ or lower, the phase of HFE is changed from the supercritical fluidto gas. Since the temperature inside of the chamber 11 is set at Ts orhigher, IPA is kept gaseous even after the phase of HFE is changed,thereby preventing reliquefaction.

(Step 5209) After the pressure inside of the chamber 11 is decreaseddown to the atmospheric pressure, the chamber 11 is cooled, and then,the semiconductor substrate is delivered out of the chamber 11.

Alternatively, after the pressure inside of the chamber 11 is decreaseddown to the atmospheric pressure, the semiconductor substrate at a hightemperature may be transported to a cooling chamber, not illustrated, asit is, followed by cooling. In this case, the chamber 11 can be kept ata certain high temperature all the time, thereby shortening the timerequired for drying the semiconductor substrate.

As described above, in the present embodiment, HFE covering the surfaceof the semiconductor substrate is changed from the liquid HFE to thesupercritical HFE, and thereafter, the supercritical HFE inside of thechamber 11 is dried in such a manner as to be directly changed in phaseto the gaseous HFE. Consequently, no capillary (i.e., the surfacetension) acts on the fine pattern formed on the semiconductor substrate,and therefore, the semiconductor substrate can be dried without breakingthe fine pattern.

Moreover, when the pressure inside of the chamber 11 is decreased sothat the supercritical HFE is changed in phase to the gaseous HFE, thetemperature inside of the chamber 11 is set to a value at which thesteam pressure of IPA becomes higher than the critical pressure of HFE,and thus, IPA staying inside of the chamber 11 is kept gaseous, to beprevented from being turned into a liquid state. In this manner, thegaseous IPA inside of the chamber 11 is liquefied to be adsorbed ontothe semiconductor substrate, thus preventing particles (i.e., dryingstains) from being produced.

Moreover, in the present embodiment, HFE staying inside of the chamber11 is heated to be turned into the supercritical state, and further, thepressure inside of the chamber 11 is decreased while keeping thetemperature inside of the chamber 11 to Ts or higher, thereby drying thesemiconductor substrate. In contrast, in the conventional supercriticaldrying method, the supercritical CO₂ fluid is continuously supplied tothe chamber for a long period of time, and then, IPA on thesemiconductor substrate and inside of the chamber is sufficientlydissolved, to be discharged little by little. IPA is sufficientlydischarged from the chamber, and then, the pressure and temperature aredecreased inside of the chamber. In the present embodiment, it isunnecessary to perform the process requiring a long period of time, inwhich the supercritical CO₂ fluid having IPA dissolved therein isdischarged from the chamber little by little, unlike the conventionalsupercritical drying method, thus shortening the time required for thedrying process.

In this manner, with the supercritical drying method for thesemiconductor substrate in the present embodiment, it is possible toreduce the particles produced on the semiconductor substrate, andfurther, to shorten the time required for the drying process.Furthermore, it is possible to reduce the cost of the chamber 11 for usein drying.

Although the description has been given of the example in which IPA isused as the water soluble organic solvent and HFE is used as the waterinsoluble organic solvent in the above-described second embodiment, thesame process may be performed even in the case of use of a water solubleorganic solvent other than IPA and a water insoluble organic solventother than HFE.

Although the temperature is increased up to Is or higher inside of thechamber 11 in step S207, before the pressure inside of the chamber 11 isdecreased in step S208 in the above-described second embodiment, thedecrease in pressure and the increase in temperature inside of thechamber 11 may be achieved at the same time as long as the temperatureinside of the chamber 11 may become Ts or higher when the HFE is changedfrom the supercritical phase to the gaseous phase.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel methods and systems describedherein may be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the methods andsystems described herein may be made without departing from the spiritof the inventions. The accompanying claims and their equivalents areintended to cover such forms or modifications as would fall within thescope and spirit of the inventions.

1.-12. (canceled)
 13. A supercritical drying method for a semiconductorsubstrate comprising: cleaning the semiconductor substrate with achemical solution; rinsing the semiconductor substrate with pure waterto cover a surface of the semiconductor substrate after the cleaning;supplying a water soluble organic solvent onto the semiconductorsubstrate after the rinsing, to replace the pure water covering thesurface of the semiconductor substrate with the water soluble organicsolvent; supplying a first water insoluble organic solvent onto thesemiconductor substrate after the replacing; introducing thesemiconductor substrate into a chamber, the surface of the semiconductorsubstrate being covered with the first water insoluble organic solvent;supplying a second water insoluble organic solvent into the chamber;setting a temperature inside of the chamber at a critical temperature ofthe second water insoluble organic solvent or higher, to turn the secondwater insoluble organic solvent into a supercritical state; and afterturning the second water insoluble organic solvent into thesupercritical state, decreasing a pressure inside of the chamber whilekeeping a temperature inside of the chamber at a predetermined valuewhich is equal to or more than a boiling point of the water solubleorganic solvent, to turn the second water insoluble organic solvent inthe supercritical state into a gaseous state, thus discharging thesecond water soluble organic solvent from the chamber.
 14. Thesupercritical drying method according to claim 13, wherein thepredetermined value is a temperature at which the steam pressure of thewater soluble organic solvent becomes higher than a critical pressure ofthe second water insoluble organic solvent.
 15. The supercritical dryingmethod according to claim 14, wherein the steam pressure of the secondwater insoluble organic solvent is higher than that of the water solubleorganic solvent.
 16. The supercritical drying method according to claim15, wherein the water soluble organic solvent includes alcohol orketone, and further, one of the first water insoluble organic solventand the second water insoluble organic solvent includes any one ofalcohol fluoride, hydrofluoroether (HFE), chlorofluorocarbon (CFC),hydrofluorocarbon (HFC), and perfluorocarbon.
 17. The supercriticaldrying method according to claim 13, wherein the first water insolubleorganic solvent is perfluorocarbon (PFC).
 18. The supercritical dryingmethod according to claim 13, wherein the second water insoluble organicsolvent is perfluorocarbon (PFC).
 19. The supercritical drying methodaccording to claim 13, wherein the predetermined value is equal to ormore than 200° C.
 20. The supercritical drying method according to claim13, wherein the water soluble organic solvent is isopropyl alcohol(IPA).
 21. A supercritical drying method for a semiconductor substratecomprising: cleaning the semiconductor substrate with a chemicalsolution; rinsing the semiconductor substrate with pure water to cover asurface of the semiconductor substrate after the cleaning; supplying awater soluble organic solvent onto the semiconductor substrate after therinsing, to replace the pure water covering the surface of thesemiconductor substrate with the water soluble organic solvent;supplying a first water insoluble organic solvent onto the semiconductorsubstrate after the replacing; introducing the semiconductor substrateinto a chamber, the surface of the semiconductor substrate being coveredwith the first water insoluble organic solvent; supplying a second waterinsoluble organic solvent into the chamber; setting a temperature insideof the chamber at a critical temperature of the second water insolubleorganic solvent or higher, to turn the second water insoluble organicsolvent into a supercritical state; and after turning the second waterinsoluble organic solvent into the supercritical state, decreasing apressure inside of the chamber while keeping a temperature inside of thechamber at a predetermined value which is equal to or more than 200° C.,to turn the second water insoluble organic solvent in the supercriticalstate into a gaseous state, thus discharging the second water solubleorganic solvent from the chamber.
 22. The supercritical drying methodaccording to claim 21, wherein the predetermined value is a temperatureat which the steam pressure of the water soluble organic solvent becomeshigher than a critical pressure of the second water insoluble organicsolvent.
 23. The supercritical drying method according to claim 22,wherein the steam pressure of the second water insoluble organic solventis higher than that of the water soluble organic solvent.
 24. Thesupercritical drying method according to claim 23, wherein the watersoluble organic solvent includes alcohol or ketone, and further, one ofthe first water insoluble organic solvent and the second water insolubleorganic solvent includes any one of alcohol fluoride, hydrofluoroether(HFE), chlorofluorocarbon (CFC), hydrofluorocarbon (HFC), andperfluorocarbon.
 25. The supercritical drying method according to claim21, wherein the first water insoluble organic solvent is perfluorocarbon(PFC).
 26. The supercritical drying method according to claim 21,wherein the second water, insoluble organic solvent is perfluorocarbon(PFC).
 27. The supercritical drying method according to claim 21,wherein the water soluble organic solvent is isopropyl alcohol (IPA).28. A supercritical drying device comprising: a cleaning unit configuredto clean a semiconductor substrate with a chemical solution; a rinsingunit configured to rinse the semiconductor substrate with pure water tocover a surface of the semiconductor substrate after cleaning thesemiconductor substrate; a supplying unit configured to supply a watersoluble organic solvent onto the semiconductor substrate after rinsingthe semiconductor substrate, to replace the pure water covering thesurface of the semiconductor substrate with the water soluble organicsolvent; a supplying unit configured to supply a first water insolubleorganic solvent onto the semiconductor substrate after replacing thepure water; a chamber; an introducing unit configured to introduce thesemiconductor substrate into the chamber, the surface of thesemiconductor substrate being covered with the first water insolubleorganic solvent; a supplying unit configured to supply a second waterinsoluble organic solvent into the chamber; a setting unit configured toset a temperature inside of the chamber at a critical temperature of thesecond water insoluble organic solvent or higher, to turn the secondwater insoluble organic solvent into a supercritical state; and adecreasing unit configured to decrease a pressure inside of the chamberwhile keeping a temperature inside of the chamber at a predeterminedvalue which is equal to or more than a boiling point of the watersoluble organic solvent, to turn the second water insoluble organicsolvent in the supercritical state into a gaseous state, thusdischarging the second water soluble organic solvent from the chamber,after turning the second water insoluble organic solvent into thesupercritical state.
 29. The supercritical drying device according toclaim 28, wherein the predetermined value is a temperature at which thesteam pressure of the water soluble organic solvent becomes higher thana critical pressure of the second water insoluble organic solvent. 30.The supercritical drying device according to claim 29, wherein the steampressure of the second water insoluble organic solvent is higher thanthat of the water soluble organic solvent.
 31. The supercritical dryingdevice according to claim 30, wherein the water soluble organic solventincludes alcohol or ketone, and further, one of the first waterinsoluble organic solvent and the second water insoluble organic solventincludes any one of alcohol fluoride, hydrofluoroether (HFE),chlorofluorocarbon (CFC), hydrofluorocarbon (HFC), and perfluorocarbon.32. The supercritical drying device according to claim 28, wherein thefirst water insoluble organic solvent is perfluorocarbon (PFC).
 33. Thesupercritical drying device according to claim 28, wherein the secondwater insoluble organic solvent is perfluorocarbon (PFC).
 34. Thesupercritical drying device according to claim 28, wherein thepredetermined value is equal to or more than 200° C.
 35. Thesupercritical drying device according to claim 28, wherein the watersoluble organic solvent is isopropyl alcohol (IPA).
 36. A supercriticaldrying device comprising: a cleaning unit configured to clean asemiconductor substrate with a chemical solution; a rinsing unitconfigured to rinse the semiconductor substrate with pure water to covera surface of the semiconductor substrate after cleaning thesemiconductor substrate; a supplying unit configured to supply a watersoluble organic solvent onto the semiconductor substrate after rinsingthe semiconductor substrate, to replace the pure water covering thesurface of the semiconductor substrate with the water soluble organicsolvent; a supplying unit configured to supply a first water insolubleorganic solvent onto the semiconductor substrate after replacing thepure water; a chamber: an introducing unit configured to introduce thesemiconductor substrate into the chamber, the surface of thesemiconductor substrate being covered with the first water insolubleorganic solvent; a supplying unit configured to supply a second waterinsoluble organic solvent into the chamber; a setting unit configured toset a temperature inside of the chamber at a critical temperature of thesecond water insoluble organic solvent or higher, to turn the secondwater insoluble organic solvent into a supercritical state; and adecreasing unit configured to decrease a pressure inside of the chamberwhile keeping a temperature inside of the chamber at a predeterminedvalue which is equal to or more than 200° C., to turn the second waterinsoluble organic solvent in the supercritical state into a gaseousstate, thus discharging the second water soluble organic solvent fromthe chamber after turning the second water insoluble organic solventinto the supercritical state.
 37. The supercritical drying deviceaccording to claim 36, wherein the predetermined value is a temperatureat which the steam pressure of the water soluble organic solvent becomeshigher than a critical pressure of the second water insoluble organicsolvent.
 38. The supercritical drying device according to claim 37,wherein the steam pressure of the second water insoluble organic solventis higher than that of the water soluble organic solvent.
 39. Thesupercritical drying device according to claim 38, wherein the watersoluble organic solvent includes alcohol or ketone, and further, one ofthe first water insoluble organic solvent and the second water insolubleorganic solvent includes any one of alcohol fluoride, hydrofluoroether(HFE), chlorofluorocarbon (CFC), hydrofluorocarbon (HFC), andperfluorocarbon.
 40. The supercritical drying device according to claim36, wherein the first water insoluble organic solvent is perfluorocarbon(PFC).
 41. The supercritical drying device according to claim 36,wherein the second water insoluble organic solvent is perfluorocarbon(PFC).
 42. The supercritical drying device according to claim 36,wherein the water soluble organic solvent is isopropyl alcohol (IPA).